The present invention relates generally to aluminum alloys and more specifically to a method for forming high strength aluminum alloy powder having L12 dispersoids therein into plate form for armor applications.
Metals for armor applications need exceptional yield and tensile strengths to resist plastic deformation as well as high fracture toughness to resist fracture during ballistic impact. Aluminum alloys are candidates because of their low density and have been used extensively since the latter half of the twentieth century as ballistic protection in all forms of battlefield structures, particularly vehicles. Popular aluminum armor systems currently in use are based on Al—Mg—Mn—Cr and Al—Zn—Mg—Zr alloy chemistries. Examples are 5083 and 7039 alloys in the cold worked and precipitation hardened conditions, respectively.
The mechanical properties of any alloy system depend directly on the microstructure. Strength is a function of grain size, alloy content, and second phase morphology and distribution. Small grain size, maximum solid solution strengthening and optimum concentration and morphology of disbursed second phases are important parameters when maximizing candidate armor systems. Aluminum alloys produced from powder precursors have small grain sizes, extended solid solubility and excellent second phase particle dispersions resulting in very high strengths and therefore, are candidates for armor applications.
Recent work with aluminum alloys containing coherent LI2 dispersed intermetallic phases that exhibit stable elevated temperature properties has shown the alloys to possess properties that make them candidates for armor applications. U.S. Pat. No. 6,248,453 discloses aluminum alloys strengthened by dispersed Al3X L12 intermetallic phases where X is selected from the group consisting of Sc, Er, Lu, Yb, Tm, and Lu. The Al3X particles are coherent with the aluminum alloy matrix and are resistant to coarsening at elevated temperatures. U.S. Patent Application Publication No. 2006/0269437 A1 discloses a high strength aluminum alloy that contains scandium and other elements that is strengthened by L12 dispersoids. L12 strengthened aluminum alloys have high strength and improved fatigue and fracture properties compared to commercial aluminum alloys. Fine grain size results in improved mechanical properties of materials. Hall-Petch strengthening has been known for decades where strength increases as grain size decreases. An optimum grain size for optimum strength is in the nano range of about 30 to 100 nm. These alloys also have lower ductility.